Information processing apparatus that calculates index indicating probability of event occurring to patient in future

ABSTRACT

An object is to accurately calculate an index indicating a probability of an event occurring to a patient in the future. A mortality risk calculation unit acquires a heart/mediastinum ratio (H/M ratio), obtained by administering a heart function diagnostic medicine to a first subject, from subject data stored in a subject data storage unit, and calculates an index indicating a probability of a predetermined event occurring to the first subject by substituting the H/M ratio acquired from the subject data storage unit into a function defined in accordance with a history of occurrences of the predetermined event to a plurality of second subjects.

TECHNICAL FIELD

This invention relates to a technique of calculating an index indicatinga probability of a predetermined event occurring to a patient with heartfailure.

BACKGROUND ART

Conventionally, processing of obtaining a function for calculating anindex related to an event that might occur in the future based on a testresult of a patient with heart failure, and calculating an indexindicating a probability of the event occurring to the patient in thefuture by using the function, has been proposed.

SUMMARY OF INVENTION Technical Problem

However, the conventionally proposed function is unable to accuratelycalculate the index indicating the probability of the event occurring inthe future.

An object of this invention is to accurately calculate an indexindicating a probability of an event occurring to a patient in thefuture.

Solution to Problem

A storage medium according to one aspect of this invention is acomputer-readable storage medium storing a program causing a computer toexecute processing of: acquiring a heart/mediastinum ratio (H/M ratio),obtained by administering a heart function diagnostic medicine to afirst subject, from subject data stored in a storage unit, andcalculating an index indicating a probability of a predetermined eventoccurring to the first subject by substituting the H/M ratio acquiredfrom the storage unit into a function defined in accordance with ahistory of occurrences of the predetermined event to a plurality ofsecond subjects.

An information processing apparatus according to one aspect of thisinvention includes: an acquisition unit that acquires aheart/mediastinum ratio (H/M ratio), obtained by administering a heartfunction diagnostic medicine to a first subject, from subject datastored in a storage unit, and a calculation unit that calculates anindex indicating a probability of a predetermined event occurring to thefirst subject by substituting the H/M ratio acquired from the storageunit into a function defined in accordance with a history of occurrencesof the predetermined event to a plurality of second subjects.

An information processing system according to one aspect of thisinvention includes: a storage unit that stores subject data including aheart/mediastinum ratio (H/M ratio), obtained by administering a heartfunction diagnostic medicine to a first subject, and a processor thatacquires the H/M ratio in the subject data from the storage device, andcalculate an index indicating a probability of a predetermined eventoccurring to the first subject by substituting the acquired H/M ratiointo a function defined in accordance with a history of occurrences ofthe predetermined event to a plurality of second subjects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an overall configuration of an information processingapparatus 1 according to an embodiment of the present invention.

FIG. 2 illustrates an example of a phantom 5.

FIG. 3 is a plan view illustrating acrylic plates of four layers of thephantom 5.

FIG. 4 illustrates a conversion function.

FIG. 5 is a flowchart illustrating a procedure of calculating theconversion function.

FIG. 6 is a flowchart illustrating a procedure of converting an H/Mratio.

FIG. 7 illustrates an overall configuration of an information processingapparatus 101 according to another embodiment of the present invention.

FIG. 8 is a flowchart illustrating a procedure of obtaining a five yearmortality risk function.

FIG. 9 is a flowchart illustrating a procedure of calculating a fiveyear mortality risk.

FIG. 10 illustrates an imaging environment selection window 70 forselecting an imaging environment.

FIG. 11 is a flowchart illustrating a procedure of calculating aconversion function.

FIG. 12 illustrates a first conversion function and a second conversionfunction.

FIG. 13 illustrates a conversion function selection window 80 forselecting a conversion function.

FIG. 14 is an explanatory diagram illustrating fluctuation of slopes ofconversion functions.

FIG. 15 illustrates a data input window 90.

DESCRIPTION OF EMBODIMENTS

An information processing apparatus according to a first embodiment ofthe present invention is described below with reference to the figures.

The information processing apparatus according to the present embodimentexecutes processing of making it possible to compare H/M ratios asdiagnosis indexes respectively calculated from images captured indifferent imaging environments with each other.

In the present embodiment, a planer image of a subject, administeredwith a cardiac function diagnostic medicine, captured in a certainimaging environment including a predetermined imaging device and aplaner image obtained by capturing an image of a phantom containing thesame medicine are used. In cases described in the following embodiments,MIBG (¹²³I-3-iodobenzylguanidine) is used as the cardiac functiondiagnostic medicine.

FIG. 1 illustrates an overall configuration of an information processingapparatus 1 according to the present embodiment. As illustrated in thefigure, in the information processing apparatus 1, at least one of aninput device 2, an output device 3, and an input/output (IO) device 4 isconnected to an information processing apparatus main body 10. Theinformation processing apparatus main body 10 is formed of a generalcomputer system including a processor and a memory for example.Components and functions, in the information processing apparatus mainbody 10, described below are each implemented by executing a computerprogram that can be stored in a computer-readable memory. This computerprogram is able to store a computer readable memory. The input device 2may be a keyboard, a pointing device, or the like for example. Theoutput device 3 may be a display device, a printer, or the like forexample. The IO device 4 may be a large capacity storage device, anetwork interface device, or the like for example.

The information processing apparatus main body 10 includes a phantomimage data storage unit 11, a digital phantom data storage unit 13, anH/M ratio data storage unit 15, a conversion function storage unit 17, asubject image data storage unit 19, a positioning processing unit 21, anROI setting unit 23, an H/M ratio calculation unit 25, a conversionfunction calculation unit 27, and an H/M ratio conversion processingunit 29.

The phantom image data storage unit 11 stores pieces of phantom imagedata as pieces of data on phantom images obtained by capturing phantomsadjusted to be under a certain imaging condition in different imagingenvironments. The phantom image data is acquired through the inputdevice 2 or the IO device 4 for example. For example, the phantom imagedata storage unit 11 stores the phantom image data for each imagingenvironment such as a first imaging environment and a second imagingenvironment and for each imaging condition. For example, the imagingenvironment is specified by a facility where the imaging device isinstalled, a model of the imaging device, a type of a collimator usedfor the imaging, and the like. The imaging condition is specified by atype of the phantom (difference of the configuration of the phantomdescribed later), an imaging direction of the phantom (front or back ina plan view of the phantom having a flat plate shape described later),and the like.

In the present embodiment, the phantom image obtained by capturing animage of the phantom under a predetermined imaging condition is used.More specifically, the phantom images are images of phantom capturedunder a plurality of imaging conditions common among the imagingenvironments. For example, in the present embodiment, the phantom imagescaptured under four different conditions in each imaging environment areused.

The common configuration of the phantom in the present embodiment willbe described below. The phantom has a flat plate shape of apredetermined thickness resembling a cross-section of the chest of ahuman body. The phantom includes an inner space where liquid can becontained. The inner space of the phantom can contain a solutionincluding medicine that is the same as that administered to the subject.The inner space of the phantom includes a human body (background) regionand, in the human body region, regions respectively corresponding toorgans such as a cardiac region, a thyroid region, a liver region, and alung region that are fluidically communicated with each other. Theconfiguration is described more in detail below with a specific example.The required organ region may differ in accordance with the type of theused medicine.

FIG. 2 illustrates an example of a phantom 5. FIG. 2A is a plan view ofthe phantom 5, and FIG. 2B is the side view of the phantom 5.

The phantom 5 illustrated in the figure has a four layer structure inwhich four transparent acrylic plates 51 to 54 are placed on top of theother in a stacked manner. The configuration of each of the acrylicplates 51 to 54 is described later. The four acrylic plates 51 to 54 aresandwiched by outer layer plates 50 that are transparent plate membersmade of the same material. The thickness of the outer layer plate 50 is10 mm for example. In the plan view illustrated in FIG. 2A, the phantom5 includes a human body region 61, a cardiac region 62, a liver region63, a thyroid region 64, and lung regions 65 (65 a and 65 b). All of theregions 61 to 65 are in fluid communication with each other as describedbelow. The communicated region is hereinafter referred to as the innerspace. The phantom 5 further includes an injection/discharge port 60.The inner space of the phantom is in fluid communication with theoutside through the injection/discharge port 60. Thus, liquid can beinjected into and discharged from the inner space of the phantom 5through the injection/discharge port 60. The injection/discharge port 60is closed by a screw plug 60 a, and thus the inner space is sealed.

FIG. 3 is a plan view illustrating the acrylic plates of four layers.

FIG. 3A illustrates the acrylic plate 51 as the first layer. The acrylicplate 51 includes an opening 51 a for forming the human body region 61.The thickness of the acrylic plate 51 as the first layer is 15 mm forexample.

FIG. 3B illustrates the acrylic plate 52 as the second layer. Theacrylic plate 52 as the second layer includes openings 52 b, 52 c, 52 d,and 52 e for respectively forming the cardiac region 62, the liverregion 63, the thyroid region 64, and the lung regions 65. The thicknessof the acrylic plate 52 as the second layer is 5 mm for example.

FIG. 3C illustrates the acrylic plate 53 as the third layer. The acrylicplate 53 as the third layer includes openings 53 b and 53 c forrespectively forming the cardiac region 62 and the liver region 63. Thethickness of the acrylic plate 53 as the third layer is 5 mm forexample.

FIG. 3D illustrates the acrylic plate 54 as the fourth layer. Theacrylic plate 54 as the fourth layer includes an opening 54 c forforming the liver region 63. The thickness of the acrylic plate 54 asthe fourth layer is 5 mm for example.

When the acrylic plates 51 to 54 are stacked, the openings positioned atthe same positions in the plan view are connected to each other in athickness direction, whereby the inner space is formed. Due to theresultant differences among the human body region 61, the cardiac region62, the liver region 63, the thyroid region 64, and the lung regions 65in the length in the thickness direction, the solutions respectively inthe regions 61 to 65 are different from each other in the depth in thethickness direction. For example, the cardiac region 62 is formed of theopenings 51 a, 52 b, and 53 b, and the thyroid region 64 is formed ofthe openings 51 a and 52 d. As a result, when the inner space is filledwith the solution at a uniform drug concentration, the regions 61 to 65are different from each other in the accumulated radioactivity amountper unit area corresponding to the thicknesses.

The thicknesses of the acrylic plates 51 to 54 as the first to thefourth layers and the outer layer plates 50 are not limited to thosedescribed above. Thus, the phantom may include the acrylic plates 51 to54 as the first to the fourth layers and the outer layer plates 50having the thicknesses different from the above described thicknesses.In the present embodiment, phantom images captured by using a pluralityof types of phantoms different from each other in the thicknesses of thefirst to the fourth layers are used. Thus, the phantom image datastorage unit 11 stores data of at least four phantom images underdifferent imaging conditions, obtained by capturing an image of the twotypes of phantoms from front and back in each imaging environment.

Referring back to FIG. 1, the digital phantom data storage unit 13stores digital phantom data. For example, the digital phantom data isacquired through the input device 2 or the IO device 4. The digitalphantom data is data indicating a shape of the actual phantom 5described above in the plan view. Thus, the digital phantom dataindicates the relative positions and the shapes of the regions 61 to 65in the phantom 5 illustrated in FIG. 2A. The digital phantom datafurther includes data for setting a region of interest (ROI) in apredetermined region. For example, the digital phantom data in thepresent embodiment includes data indicating regions for setting acardiac ROI and a mediastinum ROI.

The H/M ratio data storage unit 15 stores data on the H/M ratiocalculated by the H/M ratio calculation unit 25. The H/M ratio datastorage unit 15 may also store data on the H/M ratio acquired from theinput device 2 or the IO device 4.

The conversion function storage unit 17 stores data indicating aconversion function calculated by the conversion function calculationunit 27. For example, the conversion function storage unit 17 stores theconversion function and the identification information of the imagingenvironment before and after the conversion that are associated witheach other. The identification information of the imaging environmentmay be a combination of a facility name, a model of the imaging device,a type of the collimator, and the like. The conversion function forconverting a certain imaging environment to a theoretical H/M ratiodescribed later is associated with information indicating the conversionfrom the imaging environment before the conversion into a theoreticalvalue. The conversion function storage unit 17 may store data on theconversion function acquired from the input device 2 or the IO device 4.

The subject image data storage unit 19 stores image data of a subjectimage as a planer image obtained by capturing an image of the subjectadministered with the MIBG. For example, the subject image data isacquired through the input device 2 or the IO device 4. Each pixel valueof the subject image represents a count value in the RI. Each subjectimage is associated with information indicating the imaging environment.

The positioning processing unit 21 acquires the phantom image datastored in the phantom image data storage unit 11 and the digital phantomdata stored in the digital phantom data storage unit 13, and performspositioning processing to position the digital phantom data on thephantom image. For example, the positioning processing may be executedby using a known positioning algorithm. The digital phantom dataincludes the cardiac ROI and the mediastinum ROI respectivelycorresponding to the cardiac region and a mediastinum region in thephantom image. Thus, when the digital phantom is positioned on thephantom image data, the cardiac ROI and the mediastinum ROI areautomatically set. All things considered, the positioning processingunit 21 sets the ROIs through positioning of the digital phantom.

Thus, the standardized ROI setting to the phantom image is achieved.Thus, a higher accuracy of the H/M ratio can be achieved with nodifference between practitioners in the ROI setting.

The positioning processing unit 21 may similarly perform positioning ofthe digital phantom on the subject image stored in the subject imagedata storage unit 19.

The ROI setting unit 23 acquires subject image data from the subjectimage data storage unit 19 and sets the ROI in a predetermined region inthe subject image. For example, the ROI setting unit 23 sets the cardiacROI and the mediastinum ROI respectively to the cardiac region and themediastinum region in the subject image. For example, a method describedin PTL 1 may be used in the ROI setting. The processing executed by theROI setting unit 23 may be omitted when an operator manually sets theROIs.

When the digital phantom is positioned on the subject image by thepositioning processing unit 21, the ROI setting by the ROI setting unit23 may be omitted.

The H/M ratio calculation unit 25 calculates the H/M ratio based on thephantom image data or the subject image data. For example, the H/M ratiocalculation unit 25 calculates the H/M ratio based on the pixel values(count values) in the cardiac ROI and the mediastinum ROI set to thephantom image or the subject image. For example, the H/M ratiocalculation unit 25 calculates an average value of the count values inthe cardiac ROI and an average value of the count values in themediastinum ROI, and then calculates the ratio between the averagevalues with the average value of the count values in the mediastinum ROIbeing a denominator. The H/M ratio calculation unit 25 calculates theH/M ratio based on a target image, regardless of whether the targetimage is the phantom image or the subject image. The output device 3 maydisplay the H/M ratio calculated by the H/M ratio calculation unit 25.

The conversion function calculation unit 27 calculates a conversionfunction for converting the H/M ratio obtained from a certain imagingenvironment into an H/M ratio obtained from another imaging environmentor the theoretical H/M ratio. Data on the conversion function thuscalculated is stored in the conversion function storage unit 17.

For example, as illustrated in FIG. 4, the conversion functioncalculation unit 27 calculates a conversion function for converting anH/M ratio calculated from an image captured in a certain imagingenvironment (first imaging environment) into an H/M ratio to becalculated from an image captured in another imaging environment (secondimaging environment). The conversion function calculation unit 27 readsout from the H/M ratio data storage unit 15, data on a plurality of H/Mratios calculated from the phantom images captured under a plurality ofimaging conditions in the first imaging environment, and on a pluralityof the H/M ratios calculated from the phantom images captured under thesame imaging conditions in the second imaging environment. Then, theconversion function calculation unit 27 plots the H/M ratios on a graphillustrated in FIG. 4 with the H/M ratios under the same imagingconditions associated with each other, and performs a regressionanalysis to obtain a function for converting one of the H/M ratios intothe other.

With the conversion function, for example, H/M ratios respectivelycalculated from images captured in different facilities such as afacility including the first imaging environment and a facilityincluding the second imaging environment can be compared with eachother. Furthermore, with the conversion function calculation unit 27, aconversion function can be calculated with which an H/M ratio,calculated from an image captured in the imaging environment before achange of the imaging environment such as replacing of the imagingdevice, and an H/M ratio, calculated from the image captured by thechanged imaging device in the same facility, can be compared with eachother.

The conversion function calculation unit 27 calculates a function forstandardizing the H/M ratio calculated from an image captured in acertain imaging environment into a theoretical value independent fromany imaging environments. The conversion function calculation unit 27reads out from the H/M ratio data storage unit 15, H/M ratios calculatedfrom phantom images captured under a plurality of imaging conditions ina certain imaging environment. As the imaging conditions, theconfiguration (for example, a material, a thickness, and the like) ofthe phantom, the type, the concentration, and the like of the medicineaccommodated in the inner space are adjusted to be in predeterminedstates. The H/M ratio, obtained from a phantom image, is theoreticallydetermined based on the imaging conditions and while taking scatteringand absorption of radiation by the phantom into consideration. Thus, theconversion function calculation unit 27 performs the regression analysisbased on the H/M ratio obtained from the captured phantom image and thetheoretical H/M ratio to obtain a conversion function for converting oneof the H/M ratios into the other.

As described above, the ROIs are automatically set to the phantom imageby using the digital phantom, whereby a higher accuracy of the H/M ratiocan be achieved. In the present embodiment, the conversion function iscalculated by using the H/M ratio and thus can also be calculatedaccurately.

The H/M ratio conversion processing unit 29 acquires data on a desiredconversion function from the conversion function storage unit 17, andconverts the H/M ratio stored in the H/M ratio data storage unit 15. Forexample, the H/M ratio conversion processing unit 29 converts the H/Mratio calculated from the subject image captured in the first imagingenvironment into the H/M ratio to be calculated from the subject imagecaptured in the second imaging environment as follows. Specifically, theH/M ratio conversion processing unit 29 acquires data of a conversionfunction corresponding to this conversion from the conversion functionstorage unit 17, and uses the conversion function to execute conversionprocessing on the H/M ratio stored in the H/M ratio data storage unit15. Alternatively, the H/M ratio conversion processing unit 29 convertsthe H/M ratio calculated from the subject image captured in a certainimaging environment into the theoretical H/M ratio in a similar manner.

As described above, the conversion function is highly accurate, and thusthe H/M ratio obtained from the subject image can be converted with ahigh accuracy.

The information processing apparatus according to the present embodimenthaving the configuration described above calculates the conversionfunction and executes the conversion processing on the H/M ratio throughprocedures described below.

FIG. 5 is a flowchart illustrating the procedure for calculating theconversion function. Here, the processing calculating a function forconverting the H/M ratio obtained from the first imaging environmentinto the H/M ratio obtained from the second imaging environment and afunction for converting the H/M ratio obtained from the first imagingenvironment into the theoretical H/M ratio are described.

In the first and the second imaging environments, pieces of image dataof a plurality of phantom images captured under a predetermined imagingcondition are stored in the phantom image data storage unit 11 (S11).The image data is stored while being associated with identificationinformation indicating the imaging environment and the imaging conditionused for capturing the corresponding one of the phantom images. Thedigital phantom data is stored in the digital phantom data storage unit13 (S13). For example, the image data and the digital phantom data maybe acquired from the outside through the IO device 4. The processingthereafter can only be executed after the phantom image data and thedigital phantom data are prepared. Either one of steps S11 and S13 maybe executed first. Furthermore, any one of steps S11 and S13 may beomitted if the corresponding data has been prepared. In the presentembodiment, the processing at and after step S15 is executed after thepieces of data on a plurality of phantom images are stored in thephantom image data storage unit 11. Alternatively, the processing at andafter step S15 may be executed every time the image data on a singlephantom image is stored in the phantom image data storage unit 11.

The positioning processing unit 21 reads out image data on a singlephantom image as the processing target from the phantom image datastorage unit 11. The positioning processing unit 21 further reads outthe digital phantom data from the digital phantom data storage unit 13.The positioning processing unit 21 performs positioning of the digitalphantom on the phantom image that is the processing target. Thus, at thesame time, the ROIs are set to the cardiac region and the mediastinumregion in the phantom image (S15).

The H/M ratio calculation unit 25 calculates the H/M ratio based on thecount values in the images in the ROIs set to the phantom image in stepS15 (S19). The data on the H/M ratio thus calculated is stored in theH/M ratio data storage unit 15.

Then, the processing returns to step S15 (S21: No), whereby the H/Mratio calculation processing is repeated until the H/M ratio iscalculated for all the phantom images that are the processing targets.

When the H/M ratio is calculated for all the phantom images that are theprocessing targets (S21: Yes), the conversion function calculation unit27 reads out the pieces of data on the H/M ratios calculated from thephantom images captured from the first and the second imagingenvironments from the H/M ratio data storage unit 15, and calculates theconversion function between the two environments (S23). The conversionfunction for converting the H/M ratio obtained from the first imagingenvironment into the theoretical H/M ratio is calculated by using thetheoretical H/M ratio obtained from each imaging condition stored in theconversion function calculation unit 27 in advance. The data indicatingthe conversion function calculated by the conversion functioncalculation unit 27 is stored in the conversion function storage unit17.

The information related to the conversion function thus calculated maybe output by the output device 3.

FIG. 6 is a flowchart illustrating a procedure for converting the H/Mratio, obtained from an image of the subject captured in the firstimaging environment, by using the conversion function described above.

Image data on a subject image obtained by capturing the subjectadministered with the MIBG in the first imaging environment is stored inthe subject image data storage unit 19 (S31). For example, the imagedata may be acquired from the outside through the IO device 4. Theprocessing thereafter can be only executed after the subject image datais prepared. When the subject image data has already been prepared, stepS31 may be omitted.

The ROI setting unit 23 reads out the image data on the subject image asthe processing target from the subject image data storage unit 19. TheROI setting unit 23 further sets the ROIs to the cardiac region and themediastinum region in the subject image as the processing target (S35).

The H/M ratio calculation unit 25 calculates the H/M ratio based on thecount values in the images in the ROIs set in step S35 (S37). The dataon the H/M ratio thus calculated is stored in the H/M ratio data storageunit 15.

The H/M ratio conversion processing unit 29 reads out the data on theH/M ratio calculated in step S37 from the H/M ratio data storage unit15, and reads out the data on a desired conversion function from theconversion function storage unit 17. Then, the H/M ratio conversionprocessing unit 29 converts the H/M ratio by using the conversionfunction (S39). For example, the H/M ratio conversion processing unit 29reads out the data on the conversion function for converting the firstimaging environment into the second imaging environment from theconversion function storage unit 17, and converts the H/M ratio obtainedfrom the first imaging environment into the H/M ratio obtained from thesecond imaging environment. Alternatively, the H/M ratio conversionprocessing unit 29 reads out the data on the conversion function forconverting the H/M ratio obtained from the first imaging environmentinto the theoretical H/M ratio from the conversion function storage unit17, and converts the H/M ratio obtained from the first imagingenvironment into the theoretical value.

The H/M ratios before and after the conversion may be output by theoutput device 3.

With the present embodiment, the H/M ratios respectively calculated fromimages of the subject, administered with a diagnostic medicine such asMIBG, captured in different imaging environments can be accuratelycompared with each other. In particular, by converting the H/M ratiointo the theoretical value, the H/M ratio can be accurately standardizedinto an H/M ratio independent from the imaging environment.

An information processing apparatus according to a second embodiment ofthe present invention is described below with reference to the drawings.The components that are the same as those in the first embodiment aredenoted with the same reference numerals and the description thereofwill be omitted.

The information processing apparatus according to the present embodimentexecutes processing of obtaining a function for calculating an indexindicating a probability of the occurrence of a predetermined event. Forexample, the predetermined event in the present embodiment is living ordying of a patient with heart failure after a predetermined period (forexample, after 5 years). The index indicates whether the predeterminedevent occurs in the future, and is an index (5 year mortality risk)indicating the probability of the patient being alive after 5 years inthe present embodiment.

FIG. 7 illustrates an overall configuration of an information processingapparatus 101 according to the present embodiment. As illustrated in thefigure, in the information processing apparatus 101, at least one of theinput device 2, the output device 3, and the IO device 4 is connected toan information processing apparatus main body 110. The informationprocessing apparatus main body 110 is formed of a general computersystem including a processor and a memory for example. Components andfunctions, in the information processing apparatus main body 110,described below are each implemented by executing a computer program.The computer program can be stored in a computer-readable memory.

The information processing apparatus main body 110 includes ananalytical data storage unit 111, a subject data storage unit 113, amortality risk function storage unit 115, a logistic regression analysisexecution unit 117, and a mortality risk calculation unit 119.

The analytical data storage unit 111 stores analytical data related toregular or irregular test performed on a large number of subjects(corresponding to a second subject) with heart failure in one or aplurality of facilities. The analytical data includes the age, thegender, a heart/mediastinum ratio (H/M ratio), an index (for example,New York Heart Association (NYHA) class) indicating the severity of theheart failure, an index (for example, Left Ventricular Ejection Fraction(LVEF)) indicating a left ventricular function, and life or death after5 years. For example, the analytical data is acquired through the inputdevice 2 or the IO device 4. The age, the gender, the H/M ratio, theindex indicating the severity of the heart failure, and the indexindicating the left ventricular function correspond to subject data onthe second subject, and life or death after 5 years corresponds to eventdata.

The age is the age of each subject at the time of the test. The genderis the gender of each subject and is male or female.

The H/M ratio may be a heart/mediastinum ratio acquired from an RIplaner image obtained by detecting radioactivity from the subject thathas been administered with MIBG (¹²³I-3-iodobenzylguanidine) as adiagnostic medicine, as described in the first embodiment. The H/M ratiostored in the analytical data storage unit 111 may be data on the H/Mratio calculated by the H/M ratio calculation unit 25 in the firstembodiment, and may be a standardized H/M ratio independent from theimaging environment obtained by the conversion by the H/M ratioconversion processing unit 29. The H/M ratio stored in the analyticaldata storage unit 111 may also be an H/M ratio obtained from the secondimaging environment obtained by the conversion by the H/M ratioconversion processing unit 29.

The NYHA class indicates classes of severity of the heart failuredetermined by the New York Heart Association. More specifically, theseverity of the heart failure is classified into four classes bycomprehensively evaluating images, medical interviews, and the like:

NYHA class I: a cardiac disease patient, but no symptoms and nolimitation in ordinary activity.NYHA class II: a cardiac disease patient with slight or intermediatelimitation during ordinary activity. No symptoms at rest. Fatigue,palpitation, breathing difficulty and/or angina during ordinaryactivity.NYHA class III: a cardiac disease patient with marked limitation onordinary activity. No symptoms at rest. Symptoms duringless-than-ordinary activity, e.g. walking on flat land.NYHA class IV: a cardiac disease patient that experiences symptoms evenduring extremely mild activity, and may experience symptoms such asheart failure or angina even during rest.

The LVEF is a left ventricular ejection rate and an index indicatingcontractile force of the left ventricle. For example, the LVEF isacquired by an analysis on an ultrasonic echo image, and indicates thepercentage of the capacity of the left ventricle ejected by a singleejection.

The life or death after 5 years is data indicating whether the subjectthat has went through the cardiac function test is alive (alive or dead)5 years after the test. Thus, the data on the life or death after 5years is historic data indicating whether the predetermined event hasoccurred.

The subject data storage unit 113 stores subject data on a subject(corresponding to a first subject), as a calculation target of the 5year mortality risk described below. The subject data includes the age,the gender, the H/M ratio, the NYHA class, and the LVEF of the subjectfor example. The subject data may be the subject data on a singlesubject or may be subject data on a plurality of subjects. For example,the subject data is acquired through the input device 2 or the IO device4.

The H/M ratio stored in the subject data storage unit 113 may be data onthe H/M ratio calculated by the H/M ratio calculation unit 25 in thefirst embodiment, and may be a standardized H/M ratio independent fromthe imaging environment obtained by the conversion by the H/M ratioconversion processing unit 29. The H/M ratio stored in the subject datastorage unit 113 may also be an H/M ratio obtained from the secondimaging environment obtained by the conversion by the H/M ratioconversion processing unit 29. Any of the H/M ratios described above maybe stored in the subject data storage unit 113 and the analytical datastorage unit 111. Still, when the standardized H/M ratio independentfrom the imaging environment or the H/M ratio obtained from the secondimaging environment is stored in both of the storage units and is usedfor obtaining the 5 year mortality risk function described later and forcalculating the 5 year mortality risk, a more accurate function for the5 year mortality risk can be obtained and more accurate 5 year mortalityrisk can be calculated.

The mortality risk function storage unit 115 stores the 5 year mortalityrisk function calculated by the logistic regression analysis executionunit 117.

The logistic regression analysis execution unit 117 reads out theanalytical data stored in the analytical data storage unit 111, andexecutes a known logistic regression analysis to obtain a functionrelated to the 5 year mortality risk (5 year mortality risk=F (the age,the gender, the H/M ratio, the NYHA class, and the LVEF)). Thus, thefunction related to the 5 year mortality risk is determined inaccordance with the history of an occurrence (life or death after 5years) of the predetermined event, and is used for calculating an indexindicating the probability of the occurrence of the event in the future.The age, the gender, the H/M ratio, the NYHA class, and the LVEF in theanalytical data are independent variables (explanatory variables) in thelogistic regression analysis, and the 5 year mortality risk in theanalytical data is the dependent variable (objective variable) in thelogistic regression analysis.

The mortality risk calculation unit 119 reads out the subject datastored in the subject data storage unit 113 and the 5 year mortalityrisk function stored in the mortality risk function storage unit 115 tocalculate the 5 year mortality risk. More specifically, the 5 yearmortality risk is calculated by substituting the age, the gender, theH/M ratio, the NYHA class, and the LVEF in the subject data into the 5year mortality risk function. The 5 year mortality risk may berepresented with percentages or may be represented as alive or dead. The5 year mortality risk thus calculated may be displayed on the outputdevice 3, or may be printed and output by the output device 3.Alternatively, the 5 year mortality risk thus calculated may be storedin an unillustrated storage unit.

The information processing apparatus 101 according to the presentembodiment having the configuration described above obtains the 5 yearmortality risk function and calculates the 5 year mortality risk throughthe procedure described below (calculates an index indicating aprobability of an occurrence of the predetermined event).

FIG. 8 is a flowchart illustrating a procedure of obtaining the 5 yearmortality risk function. First of all, the analytical data related tothe tests performed on a large number of subjects with heart failure isstored in the analytical data storage unit 111 (S41). The analyticaldata may be acquired from the outside through the IO device 4. This stepmay be omitted when the analytical data has already been prepared.

Next, the logistic regression analysis execution unit 117 reads out theanalytical data stored in the analytical data storage unit 111, executesthe logistic regression analysis, and obtains the function related tothe 5 year mortality risk (5 year mortality risk=F (the age, the gender,the H/M ratio, the NYHA class, and the LVEF)) (S43). The functionrelated to the 5 year mortality risk thus obtained is stored in themortality risk function storage unit 115 (S45).

FIG. 9 is a flowchart illustrating a procedure of calculating the 5 yearmortality risk. First of all, the subject data is stored in the subjectdata storage unit 113 (S51). The subject data may be acquired from theoutside through the IO device 4. This step may be omitted when thesubject data has already been prepared.

Then, the mortality risk calculation unit 119 acquires the subject datastored in the subject data storage unit 113 (S53), and reads out the 5year mortality risk function stored in the mortality risk functionstorage unit 115 (S55). Then, the 5 year mortality risk is calculated bysubstituting the subject data (the age, the gender, the H/M ratio, theNYHA class, and the LVEF) into the 5 year mortality risk function thusread out (S57). The 5 year mortality risk thus calculated may bedisplayed on the output device 3 or may be printed and output by theoutput device 3.

In the present embodiment, the logistic regression analysis is performedwith the age, the gender, the H/M ratio, the NYHA class, and the LVEFselected as the independent variables from a large number of variablesas candidates of the independent variables. Thus, a highly accuratefunction related to the 5 year mortality risk can be obtained. Thus, ahighly accurate 5 year mortality risk can be calculated. By using astandardized H/M ratio independent from the imaging environment or theH/M ratio obtained from the second imaging environment, an even moreaccurate function related to the 5 year mortality risk can be obtained,and thus an even more accurate 5 year mortality risk cab be calculated.

Embodiments of the present inventions are examples for describing thepresent invention. The scope of the present invention is not limited tothe embodiments. Thus, the person skilled in the art can implement thepresent invention in various other forms without departing from the gistof the present invention.

For example, in the first embodiment described above, the H/M ratio iscalculated based on the phantom image data and the digital phantom data,and the conversion function is calculated based on the H/M ratio thuscalculated. Alternatively, the H/M ratios calculated in advance from thephantom image captured in and under various imaging environments andimaging conditions may be stored in the H/M ratio data storage unit 15,and the conversion function may be calculated by the conversion functioncalculation unit 27 based on the H/M ratio stored in the H/M ratio datastorage unit 15. The H/M ratios calculated from the phantom imagecaptured in and under various imaging environments and imagingconditions may be stored in the H/M ratio data storage unit 15 throughthe TO device 4.

FIG. 10 illustrates an imaging environment selection window 70 that isdisplayed on a display of the output device 3 and is used for selectingthe imaging environment.

As illustrated in FIG. 10, the imaging environment selection window 70displays a list 71 of imaging environments corresponding to the H/Mratios stored in the H/M ratio data storage unit 15. The list 71 furtherdisplays “theoretical” for calculating the function for converting theH/M ratio obtained from the first imaging environment into thetheoretical H/M ratio and the function of converting the theoretical H/Mratio into the H/M ratio obtained from the first imaging environment.When the user selects the imaging environment from the list 71 andclicks an arrow 72, the selected imaging environment is displayed on abefore conversion imaging environment display field 73 and an afterconversion imaging environment display field 74. When a conversionfunction calculation button 75 is clicked, the conversion function iscalculated as follows.

FIG. 11 is a flowchart illustrating a procedure of calculating theconversion function executed by the conversion function calculation unit27. The processing described herein is for calculating the function forconverting the H/M ratio obtained from the first imaging environmentinto the H/M ratio obtained from the second imaging environment, thefunction for converting the H/M ratio obtained from the first imagingenvironment into the theoretical H/M ratio, and the function forconverting the theoretical H/M ratio into the H/M ratio obtained fromthe first imaging environment.

The conversion function calculation unit 27 acquires, from the H/M ratiodata storage unit 15, the pieces of data on the H/M ratios correspondingto the first and the second imaging environments that have been selected(S61). Then, the conversion function calculation unit 27 calculates theconversion function between the two environments based on the acquiredpieces of data (S63). When the conversion function for converting theH/M ratio obtained from the first imaging environment into thetheoretical H/M ratio or the conversion function for converting thetheoretical H/M ratio into the H/M ratio obtained from the first imagingenvironment is calculated by using the theoretical H/M ratio for eachimage condition stored in the conversion function calculation unit 27 inadvance. For example, when the conversion function for converting theH/M ratio obtained from the first imaging environment into thetheoretical H/M ratio is calculated, an inverse function can be obtainedtherefrom as the conversion function for converting the theoretical H/Mratio into the H/M ratio obtained from the first imaging environment.Thus, the conversion function calculation unit 27 may calculate theconversion function in one direction and at the same time calculate theinverse function therefrom as the conversion function in the oppositedirection. The data indicating the conversion function calculated by theconversion function calculation unit 27 is stored in the conversionfunction storage unit 17.

When the function for converting the H/M ratio obtained from the firstimaging environment into the H/M ratio obtained from the second imagingenvironment is calculated, the conversion function F1 illustrated inFIG. 4 for directly converting the H/M ratio obtained from the firstimaging environment into the H/M ratio obtained from the second imagingenvironment may be calculated. Alternatively, a first conversionfunction F2 for converting the H/M ratio obtained from the first imagingenvironment into the theoretical H/M ratio and a second conversionfunction F3 for converting the theoretical H/M ratio into the H/M ratioobtained from the second imaging environment as illustrated in FIG. 12may be calculated. By thus calculating the conversion function forconverting between H/M ratios obtained from a predetermined imagingenvironment and the theoretical H/M ratio, an H/M ratio obtained from adesired imaging environment can be acquired by appropriately combiningtwo of a plurality of conversion functions. When an H/M ratio obtainedfrom a third imaging environment is to be converted into the H/M ratioobtained from the second imaging environment, a conversion function forthe direct conversion does not necessarily have to be calculated.Instead, a conversion function for converting the H/M ratio obtainedfrom the third imaging environment into the theoretical H/M ratio may becalculated in advance and may be combined with the conversion functionF3, whereby the H/M ratio obtained from the third imaging environmentcan be converted into the H/M ratio obtained from the second imagingenvironment. Thus, the conversion functions can be more simplyassociated with each other and can be managed more easily.

The H/M ratio stored in the H/M ratio data storage unit 15 is used asthe H/M ratio of the phantom. Alternatively, H/M ratios corresponding toa plurality of imaging environments stored in a server connected througha network may be recognized. Thus, the imaging environments may bedisplayed on the list 71 in the imaging environment selection window 70,and the H/M ratio obtained from the selected imaging environment may beacquired from the server.

In the embodiments described above, the conversion function calculationunit 27 calculates the conversion function, and the H/M ratio calculatedfrom the subject image is converted based on the conversion functionthus calculated. Alternatively, a plurality of conversion functions maybe calculated in advance and stored in the conversion function storageunit 17. Then, the H/M ratio conversion processing unit 29 may calculatethe H/M ratio of the subject based on the stored conversion function.The plurality of conversion functions may be stored in the conversionfunction storage unit 17 through the IO device 4.

FIG. 13 illustrates a conversion function selection window 80 that isdisplayed on the display of the output device 3 and is used forselecting the conversion function.

As illustrated in FIG. 13, the conversion function selection window 80displays a list 81 of the conversion functions stored in the conversionfunction storage unit 17. The imaging environments before and after theconversion respectively corresponding to the conversion functions aredisplayed on the list 81. When the user checks a checkbox 82 of theconversion function he or she wants to use and presses an OK button 83,the conversion function to be used for calculating the H/M ratio isselected.

The conversion function thus selected is used in the conversion step(S39) of converting the H/M ratio obtained from the image of the subjectcaptured in the first imaging environment as described with reference toFIG. 6. When a conversion function a for calculating the H/M ratio,obtained from an imaging environment C, from the theoretical H/M ratiois selected in FIG. 13, the H/M ratio conversion processing unit 29 mayread out data on the conversion function a and convert the theoreticalH/M ratio into the H/M ratio obtained from the imaging environment C.When a conversion function for converting the H/M ratio obtained fromthe first imaging environment into the H/M ratio obtained from thesecond imaging environment is selected, for example, as illustrated inFIG. 4, an H/M ratio (2.7) corresponding to the second imagingenvironment may be directly calculated from an H/M ratio (2.2)corresponding to the first imaging environment with the conversionfunction F1. Furthermore, as illustrated in FIG. 12, a theoretical H/Mratio (3.1) may be calculated from the H/M ratio (2.2) corresponding tothe first imaging environment with the conversion function F2, and theH/M ratio (2.7) corresponding to the second imaging environment may becalculated from the theoretical H/M ratio (3.1) with the conversionfunction F3. When the H/M ratio obtained from a desired imagingenvironment is calculated via the theoretical H/M ratio as in the lattercase, only the conversion function for converting between H/M ratiosobtained from a certain imaging environment and the theoretical H/Mratio needs to be stored. Thus, the conversion function can be moresimply associated with each other and can be managed more easily.

In the H/M ratio conversion processing illustrated in FIG. 6, thetheoretical H/M ratio of the subject may be converted into the H/M ratioof the subject in the first imaging environment by using a function forconverting the theoretical H/M ratio into the H/M ratio obtained fromthe first imaging environment. In this case, the theoretical H/M ratioof the subject is stored in step S31, and step S39 is executed withoutexecuting steps S35 and S37.

The conversion function stored in the conversion function storage unit17 is used. Alternatively, a plurality of conversion functions stored inthe server connected through the network may be recognized and displayedon the list 81 in the conversion function selection window 80. Then, theselected conversion function may be acquired from the server.

FIG. 14 is an explanatory diagram illustrating levels of fluctuation ofa slope of the conversion function for converting the theoretical H/Mratio into the H/M ratio obtained from each imaging environment.

When the H/M ratios are calculated by capturing images of the phantomfor a plurality of times in a predetermined imaging environment andunder imaging conditions, the resultant H/M ratios fluctuate. Thus, whenthe conversion function is calculated for a plurality of times, theslope of the conversion function as a linear function fluctuates asillustrated in FIG. 14. An average value is calculated by a plurality ofthe slopes, and can use for the conversion function. Thus, a moreaccurate conversion function can be obtained. Furthermore, a median or amode of the slopes may be used instead of the average value.

The conversion function may be calculated by calculating and using anaverage value of the H/M ratios obtained under the imaging conditions ina predetermined imaging environment. Alternatively, the median or themode of a plurality of H/M ratios may be used instead of the averagevalue of the plurality of H/M ratios.

In the second embodiment described above, the index related to the 5year mortality risk is calculated as the index indicating theprobability of an occurrence of the predetermined event. Alternatively,the predetermined event may be a mortality risk of any years, or thepredetermined event may be fatal arrhythmia or sudden cardiac death,rather than.

The NYHA class as the independent variable has four classes I to IV.Alternatively, the regression analysis may be performed with the NYHAclass as two categories with one including the classes I and II and theother one including the classes III and IV. Furthermore, the regressionanalysis may be performed with every ten years of age being a singlecategory.

In the embodiments described above, the processing of calculating theH/M ratio and the processing of calculating the 5 year mortality riskare separately executed. Alternatively, the processing of calculating 5year mortality risk function may be performed in advance before beingcombined with the processing of calculating the H/M ratio, so that the 5year mortality risk is calculated when the H/M ratio is calculated.

The subject data may include at least one of the H/M ratio, the age andthe gender of the subject, the index indicating the severity of theheart failure, and the index indicating the left ventricular function.In the embodiments described above, five independent variables,including the H/M ratio, the age and the gender of the subject, theindex indicating the severity of the heart failure, and the indexindicating the left ventricular function, are used in the functionrelated to the 5 year mortality risk. Alternatively, the H/M ratio maybe the only independent variable. Furthermore, the H/M ratio and atleast one of the age, the gender, the index indicating the severity ofthe heart failure, and the index indicating the left ventricularfunction of the subject may be used in the function.

In the 5 year mortality risk calculation processing in FIG. 9, thesubject data stored in the subject data storage unit 113 is acquired instep S53. Alternatively, the 5 year mortality risk may be calculated byacquiring the subject data input to a data input window 90 asillustrated in FIG. 15(A).

FIG. 15(A) illustrates the data input window 90 that is displayed on thedisplay of the output device 3 and is used for inputting the subjectdata.

As illustrated in FIG. 15(A), the data input window 90 includes asubject data input area 91, a Calc button 92, a 5 year mortality riskdisplay portion 93, and a correction checkbox 94. The age, the NYHAclass, the H/M ratio, the gender, and the LVEF of the subject as thesubject data can be input to the subject data input area 91.

When the user clicks the Calc button 92 after inputting the subjectdata, the 5 year mortality risk is calculated based on the input subjectdata and the 5 year mortality risk function stored in the mortality riskfunction storage unit 115, and the 5 year mortality risk thus calculatedis displayed on the 5 year mortality risk display portion 93.

When the correction checkbox 94 is checked as illustrated in FIG. 15(B),the H/M ratio that has been input is corrected by the H/M ratio in apredetermined imaging environment, and then the 5 year mortality risk iscalculated. The correction is executed by storing the conversionfunction for converting the imaging environment corresponding to the H/Mratio that has been input into the predetermined imaging environment orthe conversion function for converting the imaging environmentcorresponding to the H/M ratio that has been input into the theoreticalH/M ratio and the conversion function for converting the theoretical H/Mratio into the predetermined imaging environment, and reading out andexecuting the conversion functions. Thus, with standardized imagingenvironment obtained from the predetermined imaging environment, thestandardized 5 year mortality risk can be calculated. In the presentembodiment, the 5 year mortality risk changes from 25% to 35% bycorrecting the H/M ratio, as illustrated in FIG. 15.

The embodiments described above can be expressed as follows.

An information processing system includes: a storage unit that storessubject data including a heart/mediastinum ratio (H/M ratio), obtainedby administering a heart function diagnostic medicine to a firstsubject, and a processor that acquires the H/M ratio in the subject datafrom the storage device, and calculate an index indicating a probabilityof a predetermined event occurring to the first subject by substitutingthe acquired H/M ratio into a function defined in accordance with ahistory of occurrences of the predetermined event to a plurality ofsecond subjects.

In the information processing system, the subject data further includesat least one of an age, a gender, an index indicating a severity ofheart failure, and an index indicating a left ventricular function of asubject, in addition to the H/M ratio, and the processor calculates theindex indicating the probability of the predetermined event occurring tothe first subject by substituting at least one of the age, the gender,the index indicating the severity of heart failure, and the indexindicating the left ventricular function, in addition to the H/M ratio,into the function.

In the information processing system, only the H/M ratio, the age, thegender, the index indicating the severity of heart failure, and theindex indicating the left ventricular function of the first subject aresubstituted into the function.

In the information processing system, the index indicating theprobability of the predetermined event occurring is a 5 year mortalityrisk.

In the information processing system, the heart function diagnosticmedicine is MIBG (¹²³I-3-iodobenzylguanidine).

REFERENCE SIGNS LIST

-   1, 101 Information processing apparatus-   5 Phantom-   10, 110 Information processing apparatus main body-   11 Phantom image data storage unit-   13 Digital phantom data storage unit-   15 H/M ratio data storage unit-   17 Conversion function storage unit-   19 Subject image data storage unit-   21 Positioning processing unit-   23 ROI setting unit-   25 H/M ratio calculation unit-   27 Conversion function calculation unit-   29 H/M ratio conversion processing unit-   111 Analytical data storage unit-   113 Subject data storage unit-   115 Mortality risk function storage unit-   117 Logistic regression analysis execution unit-   119 Mortality risk calculation unit

1. A computer-readable storage medium storing a program causing acomputer to execute processing of: acquiring a heart/mediastinum ratio(H/M ratio), obtained by administering a heart function diagnosticmedicine to a first subject, from subject data stored in a storage unit;and calculating an index indicating a probability of a predeterminedevent occurring to the first subject by substituting the H/M ratioacquired from the storage unit into a function defined in accordancewith a history of occurrences of the predetermined event to a pluralityof second subjects.
 2. The storage medium according to claim 1, whereinthe subject data further includes at least one of an age, a gender, anindex indicating a severity of heart failure, and an index indicating aleft ventricular function of a subject, in addition to the H/M ratio,and in the calculating step, the index indicating the probability of thepredetermined event occurring to the first subject is calculated bysubstituting at least one of the age, the gender, the index indicatingthe severity of heart failure, and the index indicating the leftventricular function, in addition to the H/M ratio, into the function.3. The storage medium according to claim 1, wherein only the H/M ratio,the age, the gender, the index indicating the severity of heart failure,and the index indicating the left ventricular function of the firstsubject are substituted into the function.
 4. The storage mediumaccording to claim 1, wherein the index indicating the probability ofthe predetermined event occurring is a 5 year mortality risk.
 5. Thestorage medium according to claim 1, wherein the heart functiondiagnostic medicine is MIBG (¹²³I-3-iodobenzylguanidine).
 6. The storagemedium according to claim 1, wherein: the H/M ratio in the subject dataon the first subject is an H/M ratio obtained by conversion using aconversion function that converts an H/M ratio in the first imagingenvironment into an H/M ratio independent from the imaging environmentsor converts the H/M ratio independent from the imaging environments intothe H/M ratio in the first imaging environment; and the conversionfunction is a function that is obtained based on a first phantom H/Mratio and an H/M ratio that is independent from imaging environments andis obtained under a predetermined condition, the first phantom H/M ratiothat is an H/M ratio of a phantom in the first imaging environment beingacquired by performing, based on phantom data that is data of a phantomimage obtained by imaging the phantom under the predetermined conditionin the first imaging environment and digital phantom data that is dataof a digital phantom including a cardiac ROI and a mediastinum ROI,positioning of the digital phantom on the phantom image, and bycalculating based on the phantom data of the phantom image to which thecardiac ROI and the mediastinum ROI are set, the conversion functionconverting the first phantom H/M ratio into the H/M ratio independentfrom the imaging environments or converting the H/M ratio independentfrom the imaging environments into the first phantom H/M ratio.
 7. Thestorage medium according to claim 6, wherein the conversion function isa linear function with a slope, and the slope is any one of an averagevalue, a median value, and a mode value of a plurality of the slopes asa result of obtaining the conversion function for a plurality of times.8. The storage medium according to claim 6, wherein the processing stepsexecuted by the computer further include executing processing ofobtaining the conversion function.
 9. The storage medium according toclaim 6, wherein the processing steps executed by the computer furtherinclude executing processing of converting the H/M ratio in the firstimaging environment into the H/M ratio independent from the imagingenvironments, or converting the H/M ratio independent from the imagingenvironments into the H/M ratio in the first imaging environment, usingthe conversion function.
 10. The storage medium according to claim 1,wherein: the H/M ratio in the subject data on the first subject is anH/M ratio obtained by conversion using a conversion function thatconverts an H/M ratio in the first imaging environment into an H/M ratioin a second imaging environment; and the conversion function is afunction that is obtained: based on a first phantom H/M ratio and asecond phantom H/M ratio, the first phantom H/M ratio that is an H/Mratio of a phantom in the first imaging environment being acquired byperforming, based on phantom data that is data of a first phantom imageobtained by imaging the phantom under the predetermined condition in thefirst imaging environment and digital phantom data that is data of adigital phantom including a cardiac ROI and a mediastinum ROI,positioning of the digital phantom on the first phantom image, and bycalculating based on the phantom data of the first phantom image towhich the cardiac ROI and the mediastinum ROI are set, and the secondphantom H/M ratio that is an H/M ratio of a phantom in the secondimaging environment being acquired by performing, based on phantom datathat is data of a second phantom image obtained by imaging the phantomunder the predetermined condition in the second imaging environment andthe digital phantom data, positioning of the digital phantom on thesecond phantom image, and by calculating based on the phantom data ofthe second phantom image to which the cardiac ROI and the mediastinumROI are set.
 11. The storage medium according to claim 10, wherein theconversion function is a linear function with a slope, and the slope isany one of an average value, a median value, and a mode value of aplurality of the slopes as a result of obtaining the conversion functionfor a plurality of times.
 12. The storage medium according to claim 10,wherein the conversion function includes: a first conversion functionconverting the first phantom H/M ratio into an H/M ratio independentfrom the imaging environments; and a second conversion functionconverting the H/M ratio independent from the imaging environments intothe second phantom H/M ratio.
 13. The storage medium according to claim10, wherein the processing executed by the computer further includeprocessing of obtaining the conversion function.
 14. The storage mediumaccording to claim 10, wherein the processing executed by the computerfurther include processing of converting the H/M ratio in the firstimaging environment into the H/M ratio in the second imagingenvironment.
 15. An information processing apparatus comprising: anacquisition unit that acquires a heart/mediastinum ratio (H/M ratio),obtained by administering a heart function diagnostic medicine to afirst subject, from subject data stored in a storage unit; and acalculation unit that calculates an index indicating a probability of apredetermined event occurring to the first subject by substituting theH/M ratio acquired from the storage unit into a function defined inaccordance with a history of occurrences of the predetermined event to aplurality of second subjects.
 16. The information processing apparatusaccording to claim 15, wherein the subject data further includes atleast one of an age, a gender, an index indicating a severity of heartfailure, and an index indicating a left ventricular function of asubject, in addition to the H/M ratio, and in the calculating step, theindex indicating the probability of the predetermined event occurring tothe first subject is calculated by substituting at least one of the age,the gender, the index indicating the severity of heart failure, and theindex indicating the left ventricular function, in addition to the H/Mratio, into the function.
 17. The information processing apparatusaccording to claim 16, wherein only the H/M ratio, the age, the gender,the index indicating the severity of heart failure, and the indexindicating the left ventricular function of the first subject aresubstituted into the function.
 18. The information processing apparatusaccording to claim 15, wherein the index indicating the probability ofthe predetermined event occurring is a 5 year mortality risk.
 19. Theinformation processing apparatus according to claim 15, wherein theheart function diagnostic medicine is MIBG (¹²³I-3-iodobenzylguanidine).20. An information processing system comprising: a storage unit thatstores subject data including a heart/mediastinum ratio (H/M ratio),obtained by administering a heart function diagnostic medicine to afirst subject; and a processor that acquires the H/M ratio in thesubject data from the storage device, and calculate an index indicatinga probability of a predetermined event occurring to the first subject bysubstituting the acquired H/M ratio into a function defined inaccordance with a history of occurrences of the predetermined event to aplurality of second subjects.